In a single suction type centrifugal fan including a scroll casing, an area of a flow passage cross section is gradually enlarged in a radial direction of an impeller from a tongue portion toward a rotating direction of the impeller. With a gas blown out from the impeller, a dynamic pressure is converted into a static pressure in the casing. In such a single suction type centrifugal fan, for downsizing of the casing, an enlargement direction of the area of the flow passage cross section is not the radial direction of the impeller but an axial direction of a motor.
Hereinafter, the above conventional single suction type centrifugal fan will be described with reference to FIGS. 5A and 5B. FIG. 5A is a side view of the conventional single suction type centrifugal fan, and FIG. 5B is a front view of the same single suction type centrifugal fan.
As shown in FIGS. 5A and 5B, single suction type centrifugal fan 101 includes casing 102, and impeller 103 built in casing 102. Casing 102 includes side plate 105 including suction port 104, scroll 106, and motor fixing side plate 108 to which motor 107 is fixed. Casing 102 is formed in a spiral shape in which an area of a flow passage cross section is gradually enlarged from tongue portion 109 toward rotating direction 110 of impeller 103. The area of the flow passage cross section is an area of a radial cross section in a region surrounded by an outer peripheral side of impeller 103, an inner side of scroll 106, side plate 105, and motor fixing side plate 108.
Impeller 103 is fixed to motor 107. When impeller 103 is rotated by drive of motor 107, suction air flow 111 flows into casing 102 from suction port 104 via impeller 103. A pressure of an air blown out from impeller 103 is boosted in spiral shape casing 102, the dynamic pressure is converted into a static pressure, and the air becomes discharge air flow 113 and flows out from discharge port 112.
In general single suction type centrifugal fan 116, an area of a flow passage cross section is enlarged in a radial direction of impeller 103 due to a shape of a scroll. However, in single suction type centrifugal fan 101 described in Patent Literature 1, motor fixing side plate 108 that enlarges the area of the flow passage cross section in a rotation shaft 114 direction of motor 107 (part of region A) is formed from tongue portion 109 toward rotating direction 110. It should be noted that in FIGS. 5A and 5B, an outer shape of general single suction type centrifugal fan 116 is also shown by broken lines.
That is, with single suction type centrifugal fan 101 of Patent Literature 1, with respect to general single suction type centrifugal fan 116, by ensuring a flow passage in the rotation shaft 114 direction, an enlargement rate in the radial direction is suppressed, so that a vertical size H and a lateral size Y of casing 102 are reduced. In a case of single suction type centrifugal fan 101, air flow 115 blown out into casing 102 from a side of a main plate of impeller 103 goes toward an outer peripheral side (side of scroll 106) and spreads to a side of motor fixing side plate 108. That is, air flow 115 smoothly flows into region A along a surface of scroll 106, so that an effect (conversion from the dynamic pressure into the static pressure) due to enlargement of the area of the flow passage cross section is obtained. The part enlarged in the rotation shaft 114 direction of motor 107 (region A) is a dead space where motor 107 protrudes from casing 102. This dead space is effectively utilized, so that downsizing of single suction type centrifugal fan 101 is realized. As a result, even in a case where the casing is downsized, a decrease in performance (static pressure) is suppressed.